The Shear Viscosity and Thermal Conductivity of Nuclear Pasta

TL;DR

This paper calculates the shear viscosity and thermal conductivity of nuclear pasta in neutron star crusts using large-scale molecular dynamics simulations, revealing that non-spherical shapes do not dramatically increase viscosity.

Contribution

It introduces a semiclassical simulation approach to quantify transport properties of nuclear pasta, linking viscosity to structure factor features and comparing with spherical nuclear phases.

Findings

Viscosity increases slightly compared to spherical phases.

Viscosity is related to the static structure factor peak.

No dramatic viscosity increase from non-spherical shapes.

Abstract

We calculate the shear viscosity $\eta$ and thermal conductivity $\kappa$ of a nuclear pasta phase in neutron star crusts. This involves complex non-spherical shapes. We use semiclassical molecular dynamics simulations involving 40,000 to 100,000 nucleons. The viscosity $\eta$ can be simply expressed in terms of the height $Z^*$ and width $\Delta q$ of the peak in the static structure factor $S_p(q)$. We find that $\eta$ increases somewhat, compared to a lower density phase involving spherical nuclei, because $Z^*$ decreases from form factor and ion screening effects. However, we do not find a dramatic increase in $\eta$ from non-spherical shapes, as may occur in conventional complex fluids.